222 PROF. H. A. NICHOLSON AND DR. J. MURIE ON THE 



In the type species (Pal. OMo, vol. ii. p. 253) tlie vertical 

 pillars which traverse the mass are seen in transverse sections to 

 be solid, and to be composed throughout of granular carbonate of 

 lime. The chambers are arranged concentrically round the pillars ; 

 and there is an extremely well-developed system of water-canals 

 arranged in radiating groups, the cut ends of these appearing 

 conspicuously in vertical sections as so many large rounded 

 apertures. The range of Stylodictyon, so far as we know, does 

 not extend beyond the Devonian. "We append a short definition 

 of 8. retiforme, the only other type of this group with which we 

 are acquainted. 



Stylodictyon retiforme, Nich. & Miirie. 



Skeleton massive, composed of vertical columns, surrounded concen- 

 trically by lamina3, the interlaminar spaces being crossed by delicate 

 vertical or radial" pillars. The columns themselves are made up 

 of reticulated calcareous tissue, sometimes with a central vacant space 

 or canal; and their diameter (including that of the concentrically- 

 disposed vesicular tissue round each) varies from one to two lines. 

 They are placed about their own diameter apart ; and the interspaces 

 between them are filled with loosely reticulated tissue. No radiating 

 water-canals are present. 

 This species was collected by Mr. George Jennings Hinde, who recog- 

 nized its novelty, and kindly furnished us with specimens. It is at once 

 distinguished from S. columnare by the reticulated nature of the columns 

 which intersect the mass, and by the absence of radiating canals, as well 

 as by other points which we need not notice here. 



Form. ^ Log. — Hamilton Formation, Riviere aux Sables, Ontario, rare. 

 Coll. Hinde and Nicholson. 



(e) Stromatoceritjm, Hall (emended). 

 (Pal. K Y. vol. i. p. 48.) 

 Skeleton ("sarcodeme ") massive, composed of dense and thick 

 calcareous horizontal and concentric laminae, separated by very 

 narrow and irregular interspaces. The horizontal laminae are not 

 continuous, but are irregularly disposed ; there are no " radial 

 pillars " crossing the interlaminar spaces ; and the entire mass is 

 perforated by vertical tubes, which have no walls, are much 

 smaller than the tubes of Caunopora, and are placed at short but 

 irregular distances apart. These tubes place the successive inter- 

 laminar spaces in communication ; and though they often run 

 through many interspaces successively, they cannot be said to 

 be continuous from the top to the bottom of the mass. Surface 

 unknown. 



